| Pleurotus cornucopiae is abundant in protein, carbohydrate, fatty acid, mineral elements, vitamins and other activated elements which are good for human's health. It has uniquely practical effect on enhancing the immunity of human body, anticancer, anticoagular, delays senilly, and scalming nervers. Chromium is one of the essential trace elements for organism and the most important component of glucose tolerance factor (GTF). Chromium is likely to stimulate the metabolism of glucose, lipid, proteins and nucleic acids through increasing the appetency of insulin, the number of insulin receptor. The organic chromium is easier to be utilized by the animals, and has higher boiavailibility and little toxicity comparing to the inorganic forms. If we make good of its mycelia to accumulate Cr, the merits of Cr and Pleurotus cornucopiae can be combined, which will promote its medicinal and nutritive value and result in a brilliant market prospect.The optimization fermentation conditions of Cr-enriched Pleurotus cornucopiae were carried out using single factor experiment and orthogonal experiment. The results showed that the optimal carbon and nitrogen source were sucrose and yeast extract, respectively. The optimum fermentation medium obtained by orthogonal tests contained potato 200 g l-1, sucrose 25 g l-1, yeast extract 4.0 g l-1, KH2PO4 1.0 g l-1, MgSO4·7H2O 1.0 g l-1. The optimum fermentation conditions were as follows: chromium concentration in medium was 200 mg/l, initial pH 6.5, 160 rpm of revolution speed, 6 days of the fermentation time, 10% of inoculation volume, fermentation temperature 25°C and 100 mL liquid medium in a 250-mL Erlenmeyer flask. Under the optimum conditions, the biomass was 0.663 mg/100mL, and the highest yield of organic Cr in mycelia of Pleurotus cornucopiae was 3561.86μg/g and the enrichment rate of Cr was about 9.86%.Result of lixiviation process to separate inorganic chromium and organic chromium from Cr-accumulating Pleurotus cornucopiae showed that organic chromium content is 92.46%. The amino-acid analysis showed that the content of amino-acid of chromium-rich Pleurotus cornucopiae was more higher than common Pleurotus cornucopiae, especially the contents of lysine, methionine, leucine, isoleucine. The content of lysine, methionine, leucine, isoleucine were increased by 71%,45.3%,66.5%,75.3% comparing to the common Pleurotus cornucopiae. The essential amino acids and total essential amino acids were increased by 65.6%, 29.4%, respectively.The result about the physiological and biochemical bases of Cr-accumulating Pleurotus cornucopiae shows that the suitable concentration of chromium can improve the content and quality of the protein, amino and soluble sugar to different degree. It also can promote activity of extracellular amylase, carboxymethyl cellulase, pyrocatechol oxidase, guaiacol oxidase and laccase. The amylase activity was maximum when the concentration of CrCl3·6H2O was 100μg/mL. While the other four enzymes and the mycelium growth was significantly improved by 200μg/mL CrCl3·6H2O. Under the optimal concentration of chromium, extracellular enzymes activities increased by 2.37,2.56,2.28,2.08,2.39. There were evident differences in extracellular enzymes activities produced by Pleurotus cornucopiae and they showed different enzyme-producing peaks. Amylase appeared firstly and carboxymethyl cellulose enzyme took the second place, while laccase guaiacol oxidase and pyrocatechol oxidase finally occurred. The highest product of extracellular polysaccharide was observed at the concentration of 100μg/mL and the content of polysaccharide was 3120.96 mg/L which was 0.87 time higher than common Pleurotus cornucopiae. The mycelium growth, extracellular enzyme activity and exopolysaccharide was inhibited when the concentration of CrCl3·6H2O was even higher. |
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